Partitioned projection cathode-ray tube



April 1949' K. A. R. SAMSON ET AL 2,466,329

PARTITIONED PROJECTION CATHODE-RAY TUBE Filed March 5, 1947 FIG. 2. l5K' I I30 INVEN TORS KURT ARTHUR RICHARD SAMSON ERIC DOUGLAS MC CONNELLDENNIS MC MULLAN ATTORNEY Patented Apr. 5, 1949 2,466,329 PARTITIONEDPROJECTION CATHODE-RAY TUBE Kurt Arthur Richard Samson, Beckenham, EricDouglas McConnell, West Wickham, and Dennis MclVIullan,

to Cinema-Television Wallingford, England, assignors Limited, London,England, a corporation of England Application March 5, 1947, Serial No.732,410 In Great Britain August 2, 1946 18 Claims.

This invention relates to improvements in cathode ray tubes. Moreparticularly it relates to improvements in cathode ray tubes of the typeemployed in television receiver projection systerms.

The main object of the invention is to provide a cathode ray tube ofsuch construction that it is convenient to use within or forming part ofthe envelop of the tube optical elements formed of materials (such, forexample, as a synthetic resin) which continually exude gases when thegas pressure in the vicinity thereof is reduced to a low value.

A further object of the invention is to provide a cathode ray tube ofsuch construction that it is possible to use as a portion of theenvelope of the tube a very thin glass wall which has a minimumdeleterious effect on an optical image projected therethrough.

According to the invention there is provided a cathode ray tube of thkind employed for the projection of optical images, comprising anenvelope containing a fluorescent screen and having a wall thereofthrough which the optical image is arranged to be projected to a viewingscreen and wherein the space within the envelop is divided into twoportions, on of which has for at least a part of its boundary the innersurface of the said wall and is maintained at a higher gas pressure thanthe other, which contains the electron gun for the tube.

Again according to the invention there is provided a cathode ray tube ofthe kind employed for the projection of optical images comprising anenvelope containing a fluorescent screen and having a wall thereof,through which the optical image is projected to a viewing screen andwherein a space within the envelope bounded at least in part by the saidwall is partitioned off from the space containing the electron gun, sothat the former space can be maintained at a higher gas pressure than isnecessary for efiicient working in the space containing the electrongun.

According to a feature of the invention, the envelope also contains aconcave mirror for projecting the optical image.

According to a further feature of the invention, the wall through whichthe optical image is projected is formed so as to provide correction fordistortion of the optical image.

According to a further feature of the invention, the wall is arranged tocorrect for spherical aberration and coma in the image.

According to a still further feature of the invention, th two portionsof the space within the envelope are continuously evacuated.

The invention is particularly applicable tocathode ray tubes of the kinddescribed in a pending British application, No. 18,284/46, where a shellin the form of a portion of a sphere is incorporated to form a wall ofthe tube envelope, this shell being used to correct at least in part forthe spherical aberration and coma in the projected optical image.

The invention will be hereinafter more particularly described withreference to the accompanying drawing, comprising Figs. 1 and 2, whichillustrate, purely by way of example, dilierent embodiments of theinvention.

Referring now to Fig. 1, a cathode ray tube comprises a glass neck. 1incorporating an electron gun 2, a cylindrical metal member 4, havingsecured thereto at one end a spherical metal cover 3 having an apertureto which issealed the neck I, and sealed at the other end to the edge ofa transparent shell 5, which may have the form of a portion of a sphere,as described in the pending British application, No. 18,284/46, and isdesigned to correct at least in part-for the spherical aberration andcoma in the optical image which is projected therethrough. The image isobtained from a fluorescent screen supported within the cylinder l, on acurved support 6, aligned with neck I, and is projected through theshell 5, by means of a concave spherical mirror 1, also positionedwithin the cylinder A, and provided with a central aperture aligned withthe neck I. The mirror I and shell 5 have different radii of curvaturebut are concentric. A thin plane glass partition 8, divides the spacewithin the envelope into two parts 9 and Ill, whichare both continuouslyevacuated by means of an exhausting system H, comprising diffusion andbacking pumps. The space 9, is evacuated by the diffusion pumpand thebacking pump, while the space lil is evacuated by the backing pump. Themirror 1 is formed of glass and consequently the space ii can beevacuated so that a hard vacuum is obtained. The shell 5 may be formedof a synthetic resin (for example, the plastic known under the tradename of Perspex) which continuously exudes gas when the pressure in partit is substantially reduced. This will bev immaterial as the vacuum inspace it] need only be of the order which can be produced by the backingpump of exhausting system H and still will not interfer with theeificiency of the electron bombardment of the fluorescent screen inspace 9.

The arrangement illustrated in Fig. 1 can be modified in any of thefollowing ways without exceeding the spirit and scope of the invention.

(1) An aspherical correcting plate can be positioned between thepartition 8 and the shell at the center of curvature of the latter andcan be used to provide correction for spherical aberration and coma inaddition to that provided by the shell 5.

(2) The partition 8, instead of being made of plane glass, can comprisean aspherical plate designed to correct for spherical aberration andcoma. In this case the partition will be positioned coincident with thecenter of curvature of the shell.

(3) A thick, flat synthetic resin sheet can be substituted for the shelland the aspherical correcting plane positioned between this sheet andthe partition as in modification (1) above.

(4) A thick, fiat synthetic resin sheet can be substituted for the shell5, and the partition 8 can comprise the aspherical correcting plate asin modification (2) above.

Referring now to Fig. 2, the cathode ray tube comprises an innerenvelope in the form of a glass neck l3 (housing the electron gun, 13a)and a very thin glass main body 14, and an outer envelope in the form ofa metal cylinder It, having secured thereto a spherical metal cover !5,with a central aperture forming a gastight joint with the neck 13, and aspherical shell ll, similar to the shell 5 of Fig. 1. The inner andouter envelopes are separately evacuated by means of an exhaustingsystem 18, comprising diffusion and backing pumps. The inner envelope isevacuated by the diffusion pump and the backing pump while the outerenvelope is evacuated by the backing pump. The fluorescent screen isformed upon a convex metal support I9, which may be formed on a convexinner surface of the inner envelope or may be mounted within the innerenvelope or may be suitably sealed to the glass to form part of the wallof the envelope. The support I9, may be water cooled by means of a waterjacket 20. The pipe work extending to the water jacket 20 is not shown.

The optical image from the fluorescent screen is projected through theshell 11, by means of a concave spherical mirror 2!, which, unlike themirror I of Fig. 1, can be formed of a synthetic resin, due to the factthat it is not located in the portion of the envelope housing theelectron gun where a hard vacuum is essential. The mirror 2! and shellI! have difi'erent radii of curvature, but are positioned so as to havea common center of curvature. The shell I! will be formed of atransparent synthetic resin. As the body I l of the inner envelope canbe formed of very thin glass owing to the low gas pressure in the outerenvelope, the wall of this body will not distort the optical image totoo great an extent. The exhausting system I 8 continuously evacuatesboth the inner and outer envelopes, the outer envelope, which includesthe mirror 2| and shell n, both of which are formed of a material whichexudes gases being, as hereinbefore mentioned, connected to the backingpump.

Additional correction for spherical aberration and coma can beintroduced by positioning an aspherical correcting plate between thefluorescent screen and the shell 11, at the center of curvature of theshell. A thick, flat, synthetic resin sheet can be substituted for sheet11, when an aspherlcal correcting plate is used. The construction shownin Fig. 2 has the advantage as compared with the construction shown inFig. 1 that the space to be evacuated to the lower gas pressure can beconsiderably smaller and therefore the pumping apparatus can besimplified.

The vacuum in the space 9 of Fig. 1 or the inner envelope of Fig. 2 willbe of the order of 10- mm. of mercury and the vacuum in the space H! ofFig. 1 or the outer envelope of Fig. 2 will be of the order of .1 mm. ofmercury.

What is claimed is:

1. In a television projector, a first envelope enclosing a fluorescentscreen and an electron gun for projecting a beam of electrons thereon, asecond envelope surrounding the outside surface of a part of the wall ofthe first envelope, a transparent plastic window in said secondenvelope, means for creatin a partial vacuum inside the second envelope,means for intercepting and reflecting light from the fluorescent screento project it through said window portion of the Wall of the secondenvelope.

2. In a television projector as in claim 1, in which the first andsecond envelopes have a common portion of their walls which isrelatively thin and transparent, one side of this wall being on theinside of the first envelope and the other side thereof being on theinside of the second envelope, the wall being strong enough to withstandgas pressure against its side which is inside the second envelope equalto the pressure differential between a hard vacuum and a partial vacuum.

3. In a television which the first and projector as in claim 1, insecond envelopes are sealed together and have a common portion of theirWalls, the common portion being of sufi'icient strength to withstandatmospheric pressure on its outside when a hard vacuum has been producedwithin it, and the means for intercepting and reflecting comprises aperforated, curved mirror Within the second envelope disposed with itsperforation around the first envelope and a concave surface facingthrough the first envelope the surface of the fluorescent screen uponwhich the electron beam is projected.

4. In a television projector as in claim 1, in which the first andsecond envelopes are sealed together and have a common portion of theirwalls, the common portion being of suflicient strength to withstandatmospheric pressure on its outside when a hard vacuum has been producedwithin it and the means for intercepting and reflecting comprises aperforated, concave mirror within the second envelope disposed with itsperforation around the first envelope and its concave surface facingthrough the first envelope the surface of the fluorescent screen uponwhich the electron beam is projected, the fluorescent surface beingconvex toward the mirror and optic-ally coaxial therewith.

5. In a television projector as in claim 1, in which the first andsecond envelopes are sealed together and have a common portion of theirwalls, the common portion being of sufficient strength to withstandatmospheric pressure on its outside when a hard vacuum has been producedwithin it, and the means for intercepting and reflecting comprises aperforated, curved mirror within the second envelope disposed with itsperforation around the first envelope with a concave surface facingthrough the first envelope the surface of thefluorescent screen uponwhich the electron beam is projected, the mirror comprising a plasticmaterial.

6. In a television projector as in claim 1, in

5 which the first and second envelopes are sealed together and have acommon portion of their walls; the common portion being of sufficientstrength to withstand atmospheric pressure on its outside when ahardvacuum has been produced within it, the means for intercepting andreflectingcomprises a perforated, concave mirror within the second:envelope disposed'with its perforation around-the first envelope with aconcave surface facing through the first envelope the surface of thefluorescent screen upon which the electron beam is projected, thefluorescent surface is convex toward the mirror and optically coaxialtherewith, and the mirror comprises a plastic material.

'7. In a television projector as in claim 1, in which the first andsecond envelopes have a common portion of their walls which isrelatively thin and transparent, one side of this wall being on theinside of the first envelope and the other side thereof being on theinside of the second envelope, the wall being strong enough to withstanda positive gas pressure against its side on the inside of the secondenvelope which is equal to the pressure differential between a hardvacuum and a partial vacuum, the means for intercepting and reflectingcomprises a perforated, curved mirror facing the surface of thefluorescent screen upon which the electron beam is projected andreflecting light therefrom through the common wall as well as throughthe window portion of the wall of the second envelope, and the beam isprojected onto the screen through the perforation in the mirror.

8. In a television projector as in claim 1, in which the first andsecond envelopes have a common portion of their walls which isrelatively thin and transparent, one side of this wall being on theinside of the first envelope and the other side thereof being on theinside of the second envelope, the wall being strong enough to withstanda positive gas pressure against its side on the inside of the secondenvelope equal to the pressure differential between a hard vacuum and apartial vacuum, the means for intercepting and reflecting comprises aperforated, concave mirror facing the surface of the fluorescent screenwith which the electron beam is projected and reflecting light therefromthrough the common wall as well as through the window portion of thewall of the second envelope, the beam is projected onto the screenthrough the perforation in the mirror, and the fluorescent surface isconvex toward the concave mirror and has a common optical axistherewith.

9. In a television projector as in claim 1, in which the window portionof the second envelope comprises an optical element for correctingspherical aberrations produced by the means for intercepting andreflecting.

10. In a television projector as in claim 1, in which the window portionis of substantially uniform thickness, its inner and outer surfaces areshaped as portions of the surfaces of concentric spheres, and itcorrects, at least in part, for aberrations produced by the means forintercepting and reflecting.

11. In a television projector as in claim 1, in which the first andsecond envelopes have a common portion of their walls which istransparent, one side of this wall being on the inside of the firstenvelope and the other side thereof being on the inside of the secondenvelope, the wall being strong enough to withstand positive gaspressure against its side which is inside the second envelope equal tothe pressure differential between a hard vacuum and a partial vacuum,the common wall comprising a correcting plate for at least partiallycorrecting aberrations produced-by the means for interceptingandreflecting.

12. In a television projector, a first envelope whose walls include atleast one transparent and relatively thin portion, a fluorescent screenin the first envelope, gun means in the first envelope for producing abeam of electrons and projecting it into the screen, means for scanningthe Screen with the beam, a second envelope surrounding the outsidesurface of a thin portion of the wall of the first envelope, the secondenvelope having relatively thick walls comprising a window portion of atransparent plastic material, means for pumping gas from the spaceinside the second envelope to the space outside of it to form a partialvacuum, means for intercepting and reflecting light from the screen tocontrollably project it through a window portion of the wall of thesecond envelope.

13. In a television projector as in claim 12, in which the windowportion comprises a correcting plate for correcting at least in partaberrations produced by the means for intercepting and refleeting.

14. In a television projector as in claim 12, in

which the window portion is formed to correct, at least in part,aberrations produced by the means for intercepting and reflecting.

15. In a television projector as in claim 12, in which the first andsecond envelopes are sealed together and have a common portion of theirwalls 35 which is strong enough to withstand atmospheric pressure on itsoutside when there is a hard vacuum inside of it, the means forintercepting and reflecting comprises a perforated, spherical mirrorwhich is disposed With its perforation 40 around the first envelope andis concave toward the fluorescent screen, the screen and the mirror areseparated by the first envelope, the fluorescent screen is convex towardand optically coaxial with the mirror, and the fluorescent screen issupported on a metal support comprising part of the first envelope.

16. In a television projector as in claim 12, in which the first andsecond envelopes are sealed together and have a common portion of theirwalls which is strong enough to withstand atmospheric pressure on itsoutside when there is a hard vacuum inside of it, the means forintercepting and reflecting comprises a perforated spherical mirrorwhich is disposed with its perforation around the first envelope and isconcave toward the fluorescent screen, the screen and the mirror areseparated by the first envelope, the fluorescent screen is convex towardand optically coaxial with the mirror, the fluorescent screen issupported on a metal support comprising part of the first envelope, andcooling means are included which are adjacent to the outside surface ofthe metal screen support for cooling the fluorescent screen.

17. In a television projector as in claim 1, and

' means for producing a hard vacuum in the first envelope.

18. In a television projector as in claim 12, in which the envelopes aremade of metal except for the plastic window in the second envelope.

KURT ARTHUR RICHARD SAMSON. ERIC DOUGLAS MCCONNELL. DENNIS MCMULLAN.

(References on following page) Name Date Bowie Feb. 6, 1940 Bedford Aug.18, 1942 Epstein Sept. 15, 1942 FOREIGN PATENTS Country Date GreatBritain June 16, 1938 Great Britain Dec. 3, 1943

